Semiconductors and related low-dimensional nanostructures are extremely important in the modern world. They have been extensively studied and applied in industry/military areas such as ultraviolet optoelectronics, light emitting diodes, quantum-dot photodetectors and lasers. The knowledge of growth dynamics of semiconductor nanostructures by metalorganic chemical vapour deposition (MOCVD) is very important then. MOCVD, which is widely applied in industry, is a kind of chemical vapour deposition method of epitaxial growth for compound semiconductors. In this method, one or several of the precursors are metalorganics which contain the required elements for the deposit materials. Theoretical studies of growth mechanism by MOCVD from a realistic reactor dimension down to atomic dimensions can give fundamental guidelines to the experiment, optimize the growth conditions and improve the quality of the semiconductor-nanostructure-based devices. Two main types of study methods are applied in the present thesis in order to understand the growth dynamics of semiconductor nanostructures at the atomic level: (1) Kinetic Monte Carlo method which was adopted to simulate film growths such as diamond, Si, GaAs and InP using the chemical vapor deposition method; (2) Computational fluid dynamics method to study the distribution of species and temperature in the reactor dimension. The strain energy is introduced by short-range valence-force-field method in order to study the growth process of the hetero epitaxy. The Monte Carlo studies show that the GaN film grows on GaN substrate in a two-dimensional step mode because there is no strain over the surface during homoepitaxial growth. However, the growth of self-assembled GaSb quantum dots (QDs) on GaAs substrate follows strain-induced Stranski-Krastanov mode. The formation of GaSb nanostructures such as nanostrips and nanorings could be determined by the geometries of the initial seeds on the surface. Furthermore, the growth rate and aspect ratio of the GaSb QD are largely determined by the strain field distribution on the growth surface. / QC 20100713

The original aim of the research was to investigate the conceptual dimensions of style in tonal music in order to provide grounds for an objective, measurable categorization of the phenomenon that could be construed as the basis of a scientific taxonomy of musical styles. However, this is a formidable task that surpasses the practical possibilities of the project, which would hence concentrate on creating the tools that would be needed for the following stage. A review of previous attempts to deal with style in music provided a number of guidelines for the process of dealing with the material. The project intends to avoid the subjectivity of musical analysis concentrating on music observable features. A database of 250 keyboard scores in MusicXML format was built to the purpose of covering the whole span of styles in tonal music, from which it should be possible to extract features to be used in style categorization. Early on, it became apparent that most meaningful pitch-related features are linked to scale degrees, thus essentially depending on functional labeling, requiring the knowledge of the key of the music as a point function. Different proposed alternatives to determine the key were considered and a method decided upon. Software was written and its effectiveness tested. The method proved successful in determining the instant key with as much precision as feasible. On this basis, it became possible to functionally label scale degrees and chords. This software constitutes the basic tool for the extraction of pitch-related features. As its first use, the software was applied to the score database in order to quantify the usage of scale degrees and chords. The results indisputably showed that tonal music can be characterized by specific proportions in the use of the different scale degrees, whereas the use of chords shows a constant increase in chromaticism. Part of the material of this work appeared in the Springer-Verlag's 2006 volume of Lecture Notes in Computer Science.

Usant de certaines conditions, la croissance épitaxiale de GaN sur un large panel de substrats donne lieu à une assemblée de nanofils. Cette géométrie filaire peut permettre la croissance d'hétérostructures libres de tous défauts cristallins étendus, ce qui les rendent attractives pour créer des dispositifs de hautes performances. En premier lieu, mon travail de thèse a visé à clarifier le mécanisme de nucléation auto-organisé des nanofils de GaN sur substrat de silicium. Dans ce but, une étude approfondie de la couche tampon d'AlN, déposée préalablement à la nucléation des nanofils, a été réalisée, mettant en évidence une inattendue forte réactivité de l'Al avec le substrat. La nécessité de la polarité azote pour la croissance des nanofils de GaN a été mise en lumière, bien que des nanofils contenant dans leur cœur un domaine de polarité Ga ont également été observés. Dans ces nanofils, une paroi d'inversion de domaine est présente et a été démontrée être optiquement active, exhibant une photoluminescence à 3.45 eV. Ensuite des hétérostuctures filaires GaN/AlN ont été synthétisée pour des caractérisations structurales et optiques. Il a été montré que le mode de croissance de l'hétérostructure peut être changé en fonction du diamètre du nanofil. En dernier lieu, en prenant avantage de la géométrie cylindrique des nanofils, des mesures de diffusion de porteurs de charge ont été réalisées dans des nanofils de GaN et d'AlN. / Using specific conditions, GaN can be epitaxially grown on a large variety of substrates as a nanowire (NW) array. This geometry allows the subsequent growth of wire-like heterostructures likely free of extended defects, which makes them promising for increasing device controllability and performance. First, my PhD work has been devoted to the understanding of self-organized nucleation of GaN NWs on silicon substrates. For this purpose, a deep characterization of the growth mechanism of the AlN buffer deposited prior to NW nucleation has been done, emphasizing an unexpected large reactivity of Al with the substrate. The requirement of the N polarity to nucleate GaN NWs has been evidenced, although the possible existence of NWs hosting a Ga polar core has been observed as well. In these NWs, an inversion domain boundary is present and has been demonstrated to be optically active, having a photoluminescence signature at 3.45 eV. Next, GaN/AlN wire heterostructures have been grown for structural and optical characterization. It has been shown that by changing the wire diameter, different growth mode for the heterostructure could be reached.At last, thanks to the cylindrical geometry of NWs, the measurement of diffusion length for charge carriers in GaN and AlN NWs have been performed.

Tabagistas atendem seletivamente a estímulos ambientais relacionados ao cigarro, um processo cognitivo implícito denominado viés na atenção (VA). Contudo, não está claro se o VA persiste em ex-fumantes. Por isso, avaliou-se a influência do tempo de abstinência no VA em 62 ex-fumantes (de 50±11 anos) através de uma tarefa de atenção visual em computador. Independente do tempo de abstinência, os participantes evitaram as pistas associadas ao tabaco. Esta esquiva foi mais pronunciada em tempos de exposição maiores. Os ex-fumantes também atribuíram pouca valência emocional às imagens associadas ao cigarro e reportaram índices baixos de fissura antes e após a tarefa. O VA negativo e a menor valência emocional destas pistas podem constituir um processo de modulação da atenção típico da abstinência prolongada, no qual estratégias cognitivas são empregadas para manter este estado. Os resultados obtidos contribuem para a compreensão da cognição implícita na adição e sua importância no tratamento e prevenção do tabagismo. / Smokers selectively attend to smoking-related cues, an implicit cognitive process called attentional bias (AB). However, it is unclear whether former smokers present AB. Therefore, we evaluated the influence of abstinence time in VA in 62 exsmokers (50 ± 11 years-old) through a visual probe task. Participants avoided smoking cues despite of abstinence time. This avoidance was more pronounced in longer stimuli exposition. Former smokers also attributed little emotional valence to smoking cues and reported low craving rates both before and after the task. The negative AB and low emotional valence of smoking cues might constitute a process of attentional modulation typical of longer abstinence, in which cognitive strategies are employed to maintain this state. The results contribute to the understanding of implicit cognition in addiction and its importance to smoking treatment and prevention.

A way to follow products through the chain of production is important in the process industry and it is often solved by marking them with serial numbers. In some cases permanent markings such as dot peen marking is required. To ensure profitability in the industry and reduce errors, these markings must be read automatically. Automatic reading of dot peen markings using a camera can be hard since there is low contrast between the background and the numbers, the background can be uneven and different illuminations can affect the visibility. In this work, two different systems are implemented and evaluated to assess the possibility of developing a robust system. One system uses image analysis to segment the numbers before classifying them. The other system uses the recent advances in deep learning for object detection. Both implementations are shown to work in near real-time on a cpu. The deep learning object detection approach was able to classify all numbers correct in a image 60% of the time, while the other approach only succeeded in 20% of the time.

Quantum networks lie at the heart of distributed quantum computing and secure quantum communication - research areas that have seen a strong increase of interest over the last decade. Their basic architecture consist of stationary nodes composed of quantum processors which are linked via photonic channels. The key requirement, and at the same time the most demanding challenge, is the efficient distribution of entanglement between distant nodes. The two ground states of single spins confined in self-assembled InGaAs quantum dots provide an effective two-level system for the implementation of quantum bits. Moreover, they offer strong transition dipole moments with outstanding photonic properties allowing for the realisation of close to ideal, high-bandwidth spin-photon interfaces. These properties are combined with the benefits of working in the solid state, such as scalability and integrability of devices, to form a promising candidate for the implementation of fast entanglement distribution. In this dissertation we provide the first implementation of a unit cell of a quantum network based on single electron spins in InGaAs. We use a probabilistic scheme based on spin-photon entanglement and the erasure of which path information to project the two distant spins into a maximally entangled Bell state. The successful generation of entanglement is verified through a reconstruction of the final two-spin state and we achieve an average fidelity of $61.6\pm2.3\%$ at a record-high generation rate of $5.8\,\mathrm{kHz}$. One of the main constraints to the achieved fidelity is the limited coherence of the electron spin. We show that it can be extended by three orders of magnitude through decoupling techniques and develop a new measurement technique, allowing us to investigate the origins of the decoherence which has previously been obscured by nuclear feedback processes. Our results evidence that further extension of coherence is ultimately limited by intrinsic mechanisms closely related to local strain due to the growth method of self-assembled quantum dots. After establishing the intrinsic limits to the electron coherence we investigate the coherence properties of the single hole spin as an alternative two-level system with the potential for higher coherence times. We show that the hole spin coherence is indeed superior to the one of the electron and realise the first successful dynamic decoupling scheme implemented in these systems. We find that the decoherence at low external magnetic fields is still governed by coupling to the nuclear spins whereas it is dominated by electrical noise for fields exceeding a few Tesla. This noise source is extrinsic to the quantum dots and a better understanding offers the potential for further improvement of the coherence time. The findings of this work present a complete study of the coherence of the charge carriers in self-assembled quantum dots and provide the knowledge needed to improve the implementation of a quantum-dot based quantum network. In particular, the combination of spin-spin entanglement and the hole coherence times enable further research towards multidimensional photonic cluster states.

abstract: Complex dynamical systems consisting interacting dynamical units are ubiquitous in nature and society. Predicting and reconstructing nonlinear dynamics of units and the complex interacting networks among them serves the base for the understanding of a variety of collective dynamical phenomena. I present a general method to address the two outstanding problems as a whole based solely on time-series measurements. The method is implemented by incorporating compressive sensing approach that enables an accurate reconstruction of complex dynamical systems in terms of both nodal equations that determines the self-dynamics of units and detailed coupling patterns among units. The representative advantages of the approach are (i) the sparse data requirement which allows for a successful reconstruction from limited measurements, and (ii) general applicability to identical and nonidentical nodal dynamics, and to networks with arbitrary interacting structure, strength and sizes. Another two challenging problem of significant interest in nonlinear dynamics: (i) predicting catastrophes in nonlinear dynamical systems in advance of their occurrences and (ii) predicting the future state for time-varying nonlinear dynamical systems, can be formulated and solved in the framework of compressive sensing using only limited measurements. Once the network structure can be inferred, the dynamics behavior on them can be investigated, for example optimize information spreading dynamics, suppress cascading dynamics and traffic congestion, enhance synchronization, game dynamics, etc. The results can yield insights to control strategies design in the real-world social and natural systems. Since 2004, there has been a tremendous amount of interest in graphene. The most amazing feature of graphene is that there exists linear energy-momentum relationship when energy is low. The quasi-particles inside the system can be treated as chiral, massless Dirac fermions obeying relativistic quantum mechanics. Therefore, the graphene provides one perfect test bed to investigate relativistic quantum phenomena, such as relativistic quantum chaotic scattering and abnormal electron paths induced by klein tunneling. This phenomenon has profound implications to the development of graphene based devices that require stable electronic properties. / Dissertation/Thesis / Ph.D. Electrical Engineering 2012

Submitted by Hiolanda Rêgo (hiolandarego@gmail.com) on 2016-12-22T15:43:12Z No. of bitstreams: 1 Tese_ICS_Lia Muniz Barretto Fernandes.pdf: 1185581 bytes, checksum: a574788d65eeda6abbf9b9ce1dcc5ee9 (MD5) / Made available in DSpace on 2016-12-22T15:43:12Z (GMT). No. of bitstreams: 1 Tese_ICS_Lia Muniz Barretto Fernandes.pdf: 1185581 bytes, checksum: a574788d65eeda6abbf9b9ce1dcc5ee9 (MD5) / Doença de Newcastle é uma enfermidade viral aguda, altamente contagiosa, que acomete aves de várias espécies, considerada como uma das doenças mais importantes para a indústria avícola moderna. Ferramentas para diagnóstico e controle estão disponíveis para galinhas, porém ainda não foram desenvolvidos testes específicos para avestruzes. O presente trabalho visou padronizar testes sorológicos para a detecção de anticorpos contra a Doença de Newcastle em avestruzes e avaliar a situação soroepidemiológica de plantéis do estado da Bahia e de São Paulo. A padronização da técnica da Inibição da Hemaglutinação revelou interferência do tipo de eritrócito utilizado e demonstrou a necessidade do uso de hemácias da mesma espécie ou, alternativamente, de perus. Testes de ELISA indiretos foram desenvolvidos ou modificados para a utilização nesta espécie e, apesar de apresentarem alta correlação entre si, demonstraram baixa correlação com a HI. Foram desenvolvidos ainda os testes “western blot” e “dotblot”, que podem auxiliar na avaliação da resposta imune e facilitar a implantação de programas de controle. As amostras séricas analisadas revelaram a presença de anticorpos e, a ausência de vacinação dos animais avaliados, reforça a hipótese de que as avestruzes estão em contato com o vírus vacinal ou vírus de campo.

Submitted by Marco Antônio de Ramos Chagas (mchagas@ufv.br) on 2016-06-27T15:06:48Z No. of bitstreams: 1 texto completo.pdf: 717860 bytes, checksum: d71c1053a82b292b3ab10f06c3e68ce6 (MD5) / Made available in DSpace on 2016-06-27T15:06:48Z (GMT). No. of bitstreams: 1 texto completo.pdf: 717860 bytes, checksum: d71c1053a82b292b3ab10f06c3e68ce6 (MD5) Previous issue date: 2004-04-20 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / A avaliação de viabilidade de uso da técnica de immuno-dot blot para a detecção do vírus da dengue em homogenatos de larvas e de mosquitos Aedes aegypti e larvas de Aedes albopictus foi realizada utilizando-se soros humanos reativos para dengue e soros policlonais antidengue, produzidos em coelhos da raça Nova Zelândia imunizados com suspensões de vírus DEN-1 (Havaí) e DEN-2 (Nova Guiné) purificados e emulsificadas em adjuvante incompleto de Freund. Os resultados demonstraram que a técnica apresenta sensibilidade adequada para a detecção do vírus da dengue em homogenatos de larvas e de mosquitos A. aegypti e larvas de A. albopictus ainda que os títulos dos anti- soros sejam baixos. A presença do vírus foi detectada em larvas do mosquito A. albopictus, o que pode contribuir para o monitoramento do vírus mesmo na ausência de surtos da doença. Pode, inclusive, contribuir para estudos epidemiológicos mais amplos desse vírus por fornecer ferramenta para esses estudos. / The immuno-dot blot technique was tested and standardized for detection of dengue viruses in Aedes aegypti and Aedes albopictus larvae and mosquitoes homogenates. The experiments were carried out with dengue-reactive human sera and with anti-dengue polyclonal antisera prepared in New Zealand male rabbits immunized with DEN-1 (Hawai) and DEN-2 (New Guinea) purified virus suspensions emulsified in Freund incomplete adjuvant. Results showed that the virus can be easily detected by immuno-dot blot in A. aegypti and A. albopictus larvae and mosquitoes homogenates and suggest that this technique, for its simple procedure and easy reading, could be useful for field virus detection. Although it was recently established that these viruses can multiply in A. albopictus larvae, it is not known whether A. albopictus can indeed vector the DEN-1 and DEN-2 viruses in Brazil and, if so, under what percentages, relatively to A. aegypti mosquitoes. This study provides a tool for broader epidemiological studies of these viruses. / Dissertação antiga

Tabagistas atendem seletivamente a estímulos ambientais relacionados ao cigarro, um processo cognitivo implícito denominado viés na atenção (VA). Contudo, não está claro se o VA persiste em ex-fumantes. Por isso, avaliou-se a influência do tempo de abstinência no VA em 62 ex-fumantes (de 50±11 anos) através de uma tarefa de atenção visual em computador. Independente do tempo de abstinência, os participantes evitaram as pistas associadas ao tabaco. Esta esquiva foi mais pronunciada em tempos de exposição maiores. Os ex-fumantes também atribuíram pouca valência emocional às imagens associadas ao cigarro e reportaram índices baixos de fissura antes e após a tarefa. O VA negativo e a menor valência emocional destas pistas podem constituir um processo de modulação da atenção típico da abstinência prolongada, no qual estratégias cognitivas são empregadas para manter este estado. Os resultados obtidos contribuem para a compreensão da cognição implícita na adição e sua importância no tratamento e prevenção do tabagismo. / Smokers selectively attend to smoking-related cues, an implicit cognitive process called attentional bias (AB). However, it is unclear whether former smokers present AB. Therefore, we evaluated the influence of abstinence time in VA in 62 exsmokers (50 ± 11 years-old) through a visual probe task. Participants avoided smoking cues despite of abstinence time. This avoidance was more pronounced in longer stimuli exposition. Former smokers also attributed little emotional valence to smoking cues and reported low craving rates both before and after the task. The negative AB and low emotional valence of smoking cues might constitute a process of attentional modulation typical of longer abstinence, in which cognitive strategies are employed to maintain this state. The results contribute to the understanding of implicit cognition in addiction and its importance to smoking treatment and prevention.